- 


U.  S.  DEPAR  I'MIA  I'  I  )l    AGRICULTURE 
BUREAU  OF  WTOMOLOQT     CIRCULAR  Ho.  154. 

L.  O.  HOWARD.  Eniomologirt  *nd  Clurf  of  Burc»u. 


THE  LEAF  BLISTEB  .MITK. 


A.  L.  QUAINTANCE, 


U    V  -  1 1  , 


BUREAU   OF  ENTOMOLOGY. 

L.  O.  Howabd,  Entomologist  and  Chief  of  Bureau. 

C.  L.  Mablatt,  Entomologist  and  Acting  Chief  in  Absence  of  Chief. 

B.  s.  Clifton,  Executive   Issistant. 

W.  F.  Tastet,  chief  Clerk. 

F.  II.  Chittenden,  in  charge  of  truck  crop  andstqred  product  insect  investigations. 

A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  I>.  IIixii  u.  in  charge  of  -southern  field  crop  insect  investigations. 

F.  M.  Websteb,  in  charge  of  <■<  n<n  and  forage  insect  investigations. 

A.  L.  Quaintance,  in  charge  of  deciduous  fruit  insect  investigations. 

E.  V.  Phillips,  in  charge  of  bee  culture. 

D.  M.  Rogers,  in  charge  of  preventing  spread  of  moths.  fit  id  work. 

Roi.la  P.  Cubrie,  in  charge  of  editorial  work. 

Mabex  Oolcord,  in  charge  of  library, 

Decidvois  Fbuit  [nsect  Investigations. 

A.   I,.  Quaintance,  in  charge. 

Fred  Johnson,  S.  W.  Foster,  P.  R.  Jones,  F.  E.  Brooks.  A.  (;.  IIa.mmak.  K.  \v. 

Scott,  11.  L.  Novgaret,  It.  A.  Ctjshman,  L.  L.  Scott.  J.  B.  Gill,  A.  ('.  Bakes, 

W.  M.  Davidson,  E.  B.  Blakeslee,  W.  B.  Wood.  E.  II.  Stegleb,  F.  L.  Si.ma.n- 

ton,  entomological  assistants. 
J.  F.  Zimmeb,  X.  S.  Abbott,  YV.  H.  Sill,  cntotiwlogical  assistants,  employed  in 

enforcement  of  insecticide  act,  1910. 
ii 


: 


Crculah     No.     154. 


United  States  Department  of  Agriculture, 

BUREAU   OF   ENTOMOLOGY. 
L.   O.    HOWARD,    Entomologist  and   Chief  of   Bureau. 


THE   LEAF  BLISTER   Mill.. 

{Briophyet  pyri  Pngenstecher  > 

i:.\  a.  I.  iii  \in  i  \m  i . 
In  Charge  of  Deciduous  Fruit   Insect  Investigations. 

INTHODU"    [TON. 

Leaf  blister  mites  are  among  the  smallest  <>f  animal  forms  which 
attack  horticultural  crops.  These  minute  creatures,  only  one  one- 
hundred-and-fiftieth  of  an  inch  in  length,  are  invisible  to  the  un- 
aided eye,  and  m>  seen  under  a  good  hand  lens  appear  a-  the  merest 
-peck.  Although  the  mites  themselves  are  probably  unfamiliar  to 
most  ofchardists,  their  work  is  well  known,  to  pear  growers  and 
apple  growers,  in  the  reddish  or  greenish  pimples  <>r  blisterlike  spots 
to  Ik-  noted  in  early  spring  on  the  young  foliage  of  these  plant-. 
Later  these  blisters  become  brown  and  dead,  spotting  and  blotching 
the  leaves,  the  injury  resembling  that  due  to  leaf-spot  fungi  or  from 
-I  rays,  with  which  injury,  in  fact,  the  work  of  this  mite  i-  frequently 
confused.  When  the  creatures  are  abundanl  the  foliage  may  be 
almost  covered  with  the  blisters  or  l.p.w  n  -pot-,  and  the  usefulness  of 
the  leave-  to  the  tree  i-  thus  greatly  impaired.  Foliage  severely 
injured  will  fall  prematurely,  retarding  the  development  of  the  fruit 
and  in  extreme  cases  much  id'  the  crop  will  fall  to  the  ground.      I  S 

fig.  1.) 

The  leaf  blister  mite  i-  not  an  insect,  hut  belongs  to  that  class  of 
animal-  containing  the  spiders,  scorpions,  daddylonglegs,  etc.  and 
to  the  order  Acarina,  represented  by  such  well-known  form-  a-  the 
scah  mite  of  sheep,  the  cattle  tick,  and  the  red  spider.  It-  family, 
the  Eriophyidae  (Phytoptidse),  contain-  numerous  species,  all  of 
which  are  plant  feeders,  attacking  principally  the  hud-  and  lea 
Several  members  of  the  family  are  of  much  economic  importance. 
ntie  Landois  infests  vinifera  varieties  of  grapes  in  por- 

1 


Z  THK    LEAF    BLISTEB    MITE. 

(ions  of  Europe  and  in  California,  producing  the  so-called  "  erinose  " 
of  the  vine.  Eriophyea  padi  Nalepa  (=1?.  prurd-crumena  Walsh) 
is  the  cause  of  the  nail-like  galls  sometimes  found  on  the  leaves  of 
plum.  (Typhlodrom/us)  PhyUocoptea  oleivorus  Ashmead  infests  the 
fruit  and  foliage  of  the  orange,  producing  a  russeted  condition. 
PhyUocoptea  eomutus  Banks  feeds  upon  the  upper  surface  of  the 
leaves  of  the  peach,  so  injuring  them  as  to  give  the  foliage  a  silvery 
sheen.  PhyUocoptes  sclilecldendali  Xalepa  occurs  on  the  foliage  of 
the  apple,  and  in  Montana  very  important  injuries  have  been  at- 
tributed to  it. 


* 

[W^yr^^^SBl 

*         "'                »»-    .'«v     t*-              •'--        ~"~  •*■  /-,                             U. 

-_._.  fcjg 

s?@^ 

?r -*-           "^"-^t 

w 

7     - 

.     1 

$ 

*%        w 

* 

/ 

/ 

■ 

Fig.  1. — Apple  leaves  injured  by  the  leaf  blister  mite  (Brtophyea  i>>hi).     (Original.) 
ORIGIN   AND  DISTRIBUTION. 


The  mite  is  not  native  to  the  United  States  and  was  probably  in- 
troduced at  an  early  period,  presumably  from  Europe  on  nursery 
stock,  buds,  or  scions.  It  was  first  recorded  in  the  United  States  by 
Townend  Glover,  in  1872,  and  since  that  date  has  made  its  appear- 
ance in  the  principal  pear-growing  regions  of  the  United  States  and 
Canada.  It  is  known  to  occur  in  portions  of  Europe,  in  England. 
Russia,  and  Tasmania,  and  is  probably  present  in  other  fruit-growing 
regions  of  the  world,  being  at  the  present  time  a  truly  cosmopolitan 
pest. 


i  111    ii  \i    1:1.1-- 1  11;    Miii. 


CHAHA<    111:    IJ]     INJURE      \  M>    DESTRl't    I  l\  1  \  I  --. 

The  mile-.  pass  the  winter  on  the  trees,  under  the  bud  scales,  and 
attack  ilic  leaves  as  soon  a-  these  begin  to  «push  oul  in  the  Bpring. 
They  bore  -mall  hole-,  from  the  underside  t"  the  interior  '»f  the  leaf, 
where  they  deposit  their  eggs,  and  with  their  progeny  feed  upon  tin' 
tender  cells  of  tin1  leaf  substance.  Their  activities  within  tin-  leaf 
tissues  very  quickly  resull  in  the  developmen!  of  galls  or  swellii 
These  an-  at  (i  1-- 1  -mall,  pimple  like  eruptions,  especially  evident  on 
the  upper  surface  of  young  leaves,  whitish  in  color  on  the  apple, 
but  usually  with  a  reddish  t inge 

on    the    pear.        The    spots 

increase  in  size,  the  largest  be- 
coming a-  much  as  one-eighth  of 
an  inch  in  diameter.  On  pear 
leave-  the  -pot-,  as  a  rule,  be- 
come re.I.  often  brilliantly  col- 
ored a-  they  grow,  whereas  on 
apple  this  reddish  coloring  i-  ab- 
sent or  faint.      ( )n  the  underside 

of  the  leaf  the  oralis  are  whitish  and  blisterlike,  not  differing  much 
from  the  general  color  of  the  leaf  surface.     Later  they  turn  brownish 

or  black,  due  to  the  death  of  the  injured  leaf  cell-,  lo-e  much  of  their 

thickness,  and  some  may  become  somi  what  shrunken.  Figure  2  illus- 
trates a  gall  on  pear  leaf  a-  seen  in  cross-section,  the  normal  structure 
being  shown  at  //..•  <>  i-  tin'  opening  to  the  interior  of  the  gall  and  < 
designates  eggs  of  the  mite.  A  cro — ection  of  one  of  the  dried-up 
galls  i-  shown  in  figure  3. 


i"i..    2      1   :if  null.  In  cross  section,  of  leaf 
blister  mlti  nlng  ->f  sail :  ■ 

•  if    miii';    11.    normal    itruclure    of    leaf. 
1  a  ft  it  Boraner  | 


Fig.  ". — SectloD  of  leaf,  showing  structure  of  gall  of  ''l i-t.-r  mite  In  autumn:  <;.  OaU;  o. 
opening  of  gall'      (After  Comstock.) 

On  pear,  the  galls  occur  more  along  each  side  of  the  midrib  of  the 
leaf  and  on  apple  at  the  base  of,  and  along  the  margins  of  the  leaf. 
When  numerous,  however,  the  spots  will  merge  together,  forming 
large  patches  or  hands  of  variable  size,  often  involving  most  of  the 
leaf.  When  thus  abundant  the  leaves  may  become  more  or  less  rup- 
tured and  wrinkled,  and  in  the  case  of  the  apple  the  margins  may 
curl  up.  showing  the  underside.  Leaves  badly  infested  are  likely 
to  fall  prematurely,  resulting  al-o  in  the  dropping  of  the  fruit  from 
clusters  with  wor-t  injured  foliage.  The  fruit  and  fruit --tenis  of 
both   apple   and    pear   are   al-o   attacked,    the    light-colored    pimple- 


4  THE    LEAF    BUSTER    MITE. 

occurring  mostly  around  the  calyx  end  of  the  fruit  and  resulting  in 
no  material  injury.  The  injury  to  the  fruit-stems  is  noticeable  as 
irregular  thickenings,  and  when  severe  may  cause  some  of  the  fruit 
to  fall,  although  loss  frofn  this  source, even  in  worst  infested  orchards, 
will  not  be  great. 

FOOD    PLANTS. 

Pear  and  apple  are  the  more  common  food  plants  of  the  blister 
mite,  though  other  plants  are  attacked.  Dr.  Nalepa  records  this 
species  from  foliage  on  the  white  lx»am  tree  (Sorljus  aria  Crantz). 
the  European  mountain  ash  (Sorhux  niii-ujmria  L.).  the  wild-service 
tree  (Sorbus  torrninalis  Crantz),  the  service  berry  (Amelanchier 
vulgaris  Monch.),  and  the  common  cotoneaster  (Cotoneaster  vulgaris 
Lindl.). 

According  to  Parrott  the  mites  have  been  found  on  over  250  vari- 
eties of  apples,  injury  being  severe  on  some  well-known  commercial 
sorts,  as  Ben  Davis.  King,  Baldwin,  Rhode  Island  Greening,  and  at 
the  agricultural  experiment  station  at  Geneva,  X.  Y..  the  \Villiams 
Favorite  was  noted  to  be  especially  subject  to  attack,  the  trees  having 
been  prematurely  defoliated  for  two  successive  seasons. 

DESCRIPTION    AND    HABITS. 

The  general  appearance  of  the  blister  mite  is  shown  in  figure  4 
in  dorsal  and  ventral  views.  The  mite  is  microscopic  in  size,  measuring 
on  the  average  about  one  one-hundred-and-fiftieth  inch  in  length, 
whitish  in  color,  a  few  individuals  pinkish.  The  abdomen  slopes 
gradually  toward  the  posterior  end  and  is  numerously  ringed.  There 
are  only  two  pairs  of  legs,  and  these  and  the  body  bear  setae,  which 
from  their  character  and  location  are  of  importance  in  the  deter- 
mination of  species  in  this  group,  as  are  also  the  number  and  charac- 
ter of  rings  on  the  abdomen.  The  young,  except  in  size,  bear  a  gen- 
eral likeness  to  the  adults,  and  the  eggs,  though  proportionately 
large  as  compared  in  size  with  the  parent,  are  only  46  microns 
through  the  greater  diameter.  These  are  whitish,  translucent,  with 
rounded  ends,  and  are  deposited  in  the  interior  of  the  galls  (see  fig.  2). 
The  resulting  larvae  feed  upon  the  cellular  leaf  substance,  working 
out  in  various  directions,  though  they  are  not  especially  active. 

The  mites  are  to  be  found  on  the  foliage  from  their  appearance 
in  spring  until  fall,  and  several  generations  are  evidently  produced 
in  a  season.  Hibernation  occurs  under  the  bud  scales,  the  mites  often 
congregating  in  colonies  of  50  or  more.  They  become  active  in  the 
spring  often  before  the  buds  burst,  congregating  around  the  base  of 
hud  scales,  where  they  feed,  many  molting  at  this  time.  "With  the 
bursting  of  the  buds  and  the  pushing  out  of  the  tender  leaves,  these 
are  attacked  and  the  characteristic  blisterlike  spots  soon  develop. 


I  ill     i.l  \r    BLIS  III:    MM  E. 


Notwithstanding  the  minute  size  of  these  creatures,  they  fall  prey 
in  considerable  numbers,  as  observed  by  Prof.  Parrotl  in  Nev  ">  nrl, 
State,  to  the  attack  of  a  mite  '  N-  itu  pomi  Parrotl  i  which  he  thinks 
materially  assists  in  reducing  their  numbers. 


M  I   i  Hi  >n>    {)]     CONTHOI 


The  leaf  blister  mite  will  yield  to  thorough  treatment  with  kero- 
sene emulsion,  miscible  oils,  i>r  Lime-sulphur  washes.     The  d 


er  mite   [BHophj/m  pyri)  :   i.  Dona]   vi.'w:   _•.  rentral   rlew.     QreaUj 
enlarged      i  After  Nal<  p 

these  sprays,  as  for  the  Sun  Jose  scale,  should  also  protect  orchards 
from   important   injury   from  the  mites.     When   it  -;irv  to 

spray  for  the  mites  alone,  and  in  cases  of  severe  infestation,  as  has 
been  notfil  in  apple  orchards  in  New  York  State,  two  treatments 
have  been  recommended  l>y  Parrott,  using  standard  kerosene  emul- 
sion diluted  with  ."»  parts  of  water.  One  application  should  be  given 
in  late  fall  as  soon  as  most  of  the  leave-  have  fallen  and  another  the 
following  spring  before  the  trees  put  out  foliage.  If  lM>th  the  fall 
and  spring  application-  are  uot  practicable,  the  preference  should  be 


UNIVERSITY  OF  FLORIDA 


b  Tin:  LEA*  blister  1  3  1262  09216  5959 

given  to  fall  treatment.  At  this  time  many  of  the  mites  have  not  yel 
gQne  to  the  bud  scales,  hut  occur  in  the  pubescence  of  the  young 
wood  and  are  hence  more  easily  killed. 

Lime-sulphur  washes  arc  excellent  treatment-  for  these  mites  and 
their  employment  is  perhaps  preferable  as  avoiding  danger  of  injury 
to  fruit  buds  by  the  oil  sprays.  If  a  lime-sulphur  wash  is  employed, 
it  should  be  applied  with  great  thoroughness,  completely  coating  the 
tree  so  thai  when  spraying  is  finished  the  tree  will  appear  as  if 
whitewashed.  The  homemade  wash,  according  to  the  old  formula, 
lime  20  pounds,  sulphur  15  pounds,  and  water  to  make  50  galL 
will  be  quite  effective;  or  the  homemade  or  commercial  concentrate 
may  he  used.  The  former  may  be  made  according  to  the  formula. 
lime  50  pounds,  sulphur  LOO  pounds,  and  water  to  make  50  gallon-. 
When  thus  prepared  the  concentrate  should  be  used  at  the  rate  of  one 
part  to  9  or  10  parts  of  water.  Applications  of  these  washes  may 
also  be  made  in  the  fall  as  described  for  kerosene  emulsion  and  in 
the  spring,  and  if  only  one  treatment  is  to  he  given  the  spring  appli- 
cation is  preferable,  as  it  takes  the  place  of  the  first  application  of 
a  fungicide  for  apple  scab.  When  the  mite  is  quite  troublesome  both 
fall  and  spring  treatments  would  insure  its  control  more  quickly  and 
completely. 

On  the  pear  the  mites  may  be  kept  reduced  to  an  important  extent 
simply  by  searching  out  in  the  spring  branches  bearing  worst  infested 
leaves,  pruning  these  oil'  and  burning  them,  or  sprays  may  be  em- 
ployed exactly  as  indicated  for  the  apple,  if  this  is  considered 
necessary. 

Except  in  cases  of  serious  infestation  special  spraying  for  the 
Mister  mite  will  not  be  necessary.  As  to  whether  or  not  it  i-  advisa- 
ble to  spray,  the  orchardists  will  have  to  decide  after  determining  as 
exactly  as  is  possible  the  amount  of  injury  being  done  by  the  mites, 
and  care  should  be  taken  not  to  confound  with  it-  injury  that  which 
has  resulted  from  fungicidal  or  Paris-green  sprays,  and  from  leaf- 
spot  (li-ease-. 

Approved  : 

James  Wilson, 

Secrt  tary  of  .  Vgriculture. 
Washington,  I).  C,  April  /<>.  1912. 


ADDITIONAL  COPIES  of  this  publication 
XV  may  be  procured  from  the  SUPERINTEND- 
ENT of  Documents,  Government  Printing 
Office,  Washington,  D.  C. ,  at  .">  cents  per  copy 


